The present invention relates to casement window hinges and in particular to a casement window hinge reducing sash sag.
Casement window hinges allow a window to open by pivoting about a vertical axis that moves inward as the window opens. This combination motion is provided by special casement window hinges supporting the window sash. A separate operator moves the window as mounted on the hinges, typically using a crank mechanism.
Casement window hinges typically employ a two-bar linkage of a sash arm and guide arm. The sash arm is attached along the window sash, for example, by countersunk wood screws directed up through the sash arm into the wood of the sash. An inward end of the sash arm is pivotally attached to a slide that may move along a track attached to the window opening and that defines the movable pivot point of the window. A center of the sash arm is pivotally attached to one end of a guide arm whose remaining end of the guide arm is pivotally attached to the track displaced from the slide.
The sash arm and guide arm can be subject to large forces, for example, during shipping, installation, or when the window is subject to wind loads. For this reason, the sash arm and guide arms are typically fabricated out of a sturdy material such as stainless steel. They are connected together, typically, by a metal rivet that is lightly staked to allow the parts to pivot. Normally the slide is also riveted to the sash arm.
A typical casement window has a total sash weight of 30 to 160 pounds and when closed may be supported by a one inch wide slide at the edge of the sash. This support point may be 10 to 20 inches from the center of gravity of the window. The offset between the support point and the center of gravity tends to tilt the top of the sash downward, the hinging side of the sash away from the support frame, and the bottom of the sash downward towards the support frame. Looseness in the hinge joints or the attachment screws in the hinge track from aging wood, or in the hinge arms, will allow more tilt. Size on size attachment screws and tight hinge joints minimizes the tilt but nevertheless ultimately still permit the sash to sag over time under weight of the glass. This sagging causes a deformation of the window from a true rectangle and can prevent closing the window to fit within the rectangular window opening without interference between the window and the opening and/or the casement window hinges.
Accordingly, it is known to attach the guide arm to the track or window opening with an eccentric pivot pin allowing the guide arm of the lower casement window hinge to be shortened to provide an upward lifting force on the sash as it is closed helping to lift it into position. Significant amounts of sash sag over time can impose substantial compression on the guide arm and its pivot point, requiring stronger materials to resist buckling and pivot pins requiring greater adjustment forces to prevent unwanted movement of the pivot pins under greater guide arm forces.